resmgr list-installed: determine correct list of installed processors

[bertsky]

Currently, during a Docker build of ocrd/all:medium, we get:

#17 [13/17] RUN ocrd resmgr list-installed
#17 17.22 19:08:16.861 ERROR ocrd.utils.get_moduledir - ocrd-sbb-binarize --dump-module-dir failed: [Errno 2] No such file or directory: 'ocrd-sbb-binarize'
#17 17.22 19:08:16.866 ERROR ocrd.utils.get_ocrd_tool_json - ocrd-sbb-binarize --dump-json produced invalid JSON: [Errno 2] No such file or directory: 'ocrd-sbb-binarize'

IIUC This means that because we have ocrd-sbb-binarize in the preinstalled resource_list.yml, and resmgr does not (to date) utilise any ocrd-all-tool.json, it just assumes that ocrd-sbb-binarize must be present.